1. Field of the Invention
The present invention relates to a frame-by-frame color image pickup apparatus comprising means for reading an image signal for each of the reference colors in a time series fashion, an image pickup device for switching cells being read, and a memory for making concurrent the image signals of the reference colors that have been read in a time series fashion.
2. Related Art Statement
The following two types of frame-by-frame color image pickup apparatuses are known. For simplicity, the following discussion assumes that the three reference colors are red (R), green (G) and blue (B).
FIG. 10 is a simplified block diagram showing a typical conventional frame-by-frame color image pickup apparatus 31.
An image pickup device 33 is arranged at the image plane in perpendicular alignment to the optical axis of an imaging lens or an image forming lens 32 for forming an optical image of an unshown subject, a rotating filter 34 having color filters that respectively transmit R, G and B light rays is mounted between the imaging lens 32 and the image pickup device 33, and the rotating filter 34 is driven by unshown driving means such as a motor.
By rotating filter 34, the R, G and B color filters are sequentially positioned in the light path, and optical images of R, G, and B wavelength components are formed on the image pickup device 33. In response to a scan signal in synchronization with the irradiation period of each of the R, G, and B light wavelengths, from a scanning control module 35, the image pickup device 33 performs photoelectrical conversion to output, in a time series fashion, signals corresponding to the image of each wavelength component (referred to as R, G and B signals).
Time-series R, G, and B signals are A/D-converted by an A/D converter 36 into corresponding digital R, G, and B signals, which are then sequentially stored in respective color memories 38R, 38G, and 38B under the control of a memory control module 37. These signals are read at the same timing and become concurrent color image data. The concurrent color image data is fed to a signal processing module 39 to be processed into R, G and B color signals. The R, G and B color signals are then fed to an unshorn color monitor display, where the image of the subject is presented in color or fed to an image recording apparatus to be recorded there.
Referring to a timing diagram shown in FIG. 11, an X-Y address type solid-state pickup device as the image pickup device 33 is scanned in a noninterlace fashion.
As shown in FIG. 11, the rotating filter 34 rotates by a full revolution over a period of 9T, and each of the R, G, and B color filters is present in the optical path for a period of approximately 3T with switching periods being approximately 1T. As shown, R-1, for example, represents a light ray that is incident to the image pickup device 33 via the R color filter during a first cycle of revolution. Thus, during a n-th cycle of revolution, an incident light ray through an I (I=R, G, or B) color filter is represented by I-n. Also shown are an effective output signal In the image pickup device 33 outputs to each of the memories 38R, 38G, and 38B, and output signals output by the memories 38R, 38G, and 38B.
The incident light ray transmitted through the rotating filter 34 sequences through R-1, G-1, B-1, R-2, G-2, B-2, R-3, . . . . Since during each of the durations t=0-T, 3T-4T, 6T-7T, . . . , 3nT-(3n+1)T, . . . , each switching section of the R, G, and B color filters transverses the optical path or in front of the image pickup device 33, the incident light rays are mixed in color. Represented by T here is a one frame period, and n=0, 1, 2, . . . .
Effective signals free from mixed color in response to the R, G, and B incident light rays are signals R1, G1, B1, R2, . . . , which are stored and read during each of the durations t=T-3T, 4T-6T, 7T-9T, . . . , (3n-2)T-3nT, . . .
The effective output signals R1, G1, B1, R2, . . . are A/D converted through the A/D converter 36, and then written onto the R memory 38R, G memory 38G, and B memory 38B for concurrency processing.
Digital R, G, and B signals are read from the memories 38R, 38G, 38B at the same timing, and are thus concurrency processed. The same signal is read from each of the memories 38R, 38G, and 38B a plural number of times until they are updated with the next effective signals. Concurrency processed signals are then subjected to required signal processings through the signal processing module 39.
Japanese Unexamined Patent Publication No. 7-79448 discloses another known technique. In this disclosure, a frame-by-frame color camera has been proposed in which an image corresponding to one field of each color is read from an image pickup device every cycle of revolution of a rotating filter, a determination of whether the image is still or dynamic is made, and one frame is constructed over two cycles of revolution when the image is still, or one frame is constructed by correlating one field with an image of another field resulting from one revolution when the image is dynamic. For the dynamic image, frame displaying is made possible over every cycle of revolution of the rotating filter to increase an image pickup rate in the frame-by-frame method and thus to reduce color breakup.
In the above known frame-by-frame color image pickup apparatus, if a subject moves while the R, G, and B tri-color signals are being stored in respective memories for concurrency processing, R, G, and B output images will fail to coincide with each other, causing color breakup and image blurring.
To solve this problem, the apparatus disclosed in Japanese Unexamined Patent Publication 7-79448 displays a frame using one field image within the time of one cycle of revolution of the rotating filter when the image is dynamic, but is subject to the image pickup rate limitation determined by a field. The disclosure states nothing about noninterlace scanning.